I am much reassured by your support for a senile old man and I truly do not believe that geology can give us pin point accuracy about ancient temperatures :)What I see at the moment is that Paul does not believe proxy evidence can give any useful figures for temperature, particularly over long time periods but this is a theory not a fact (yet).

you completely misunderstand my evidence and position. With careful experimentation and measurement it is possible to determine temperature from appropriate proxies. For example, it is my view that the Phanerozoic marine isotope record determined by Veizer and co-workers can be interpreted as a temperature record and this record shows that on the time scale of tens to hundreds of millions of years temperature is decoupled from CO2. However, one must be cognisant of the fact that the interpretation is limited by our lack of understanding of the evolution of ocean oxygen isotope composition through geological time. One must always be open about the limitations and fully aware of the nature of possible errors and their impact on precision and ultimately interpretation of the data.. This is what I have tried to highlight in my posts. Such awareness has been conspicuously absent, or willfully ignored in many studies that combine proxies to produce a long chronology.

New isotopic tools are being developed that hold the promise of a 'thermodynamic' proxy. By that I mean a proxy whose response to temperature can be determined a priori from thermodynamic considerations. Measurement of the proxy value can then be used to estimate temperature much like the thermal expansion of mercury in a thermometer. These techniques are 'orthogonal' to the standard oxygen isotope thermometer and so decouple the temperature estimate from knowledge of the ocean isotope composition.

I see two complementary approaches. The first would be to reproduce the extensive marine oxygen isotope data set for the Phanerozoic. This will allow us to develop a long chronology for Earth's surface temperature. The second would be a series of deductive experiments targeting specific predictions of the current paradigm of a CO2 control knob.

Each would be very major undertakings and require many years, if not tens of years of effort. I'm not sure it would be possible to do on an ad hoc basis. The experiment would require many tens of thousands of measurements at the highest possible precision. It would need dedicated instruments etc. It would need access to, and collection of pristine fossil material with appropriate meta-data. Not with standing these caveats the thought of conducting such a programme regularly interests me. Some attempts have been made over the past few years but the quality of the data has not been sufficient to provide unambiguous interpretations.

It will probably remain ambiguous. As a biologist one gets used to complex multifactorial systems and the problems of trying to extract the effect of one factor from all the others. Regrettably one becomes resigned to making the best of it.

On another tack, I was just reading the final version of Hansen et al (2016), download availably here . They make considerable use of Eemion paleo data. I would welcome your opinion of its validity.

The gist is that we can expect a lower rate of warming than the IPCC A1B scenario, but much higher rates of sea level rise.

I tend to think in terms of energy flow, which makes me interested in their reasoning. The key to the authors' projection is a massive increase in the rate of ocean heat uptake by the deep oceans in the latter 21st century as freshwater melt from Greenland and Antarctica disrupt the AMOC. Curiously this produces a big temporary increase in the TOA imbalance and a temporary drop in temperature. The deniers will love it!

One concern.Their models predict South Atlantic cooling and a cold spot off Greenland in 50 years Both are already visible .

The time frame, and likely costs, would exclude such a project from climate science's pressing need, a quick easy win. The fact that a 'win' could not be guaranteed for climate science purposes, probably doesn't help either.

This is not about cherry picking data, but choosing not to plant an unknown cherry tree sapling, in case the eventual fruit, turns out to be unpalatable.

EM, thank you for the link to the Hansen et al paper. I'll certainly look at it but you'll forgive me if it takes a few weeks. It's over 50 pages long. However, having read the abstract I'd say there is nothing really new in it. People have been hypothesing for a long time about freshwater inputs and shutdown of the ocean circulation with consequent effects on ventilation and CO2 levels. People have also been interested for some time in the Eemian as a possible analogue for the present day, especially the end Eemian. We've known that Eemian temperatures have been generally warmer but don't have any degree of precision on how warm. Is it 0.5, 1.0, 1.5, 2 degrees? It is actually very difficult to determine. We have also known that the Eemian climate appears more unstable than our own. Finally there is very good evidence that Eemian sea levels are higher than at present by several metres and that there were periods when tere might have been rapid steps in sea level. Again, as with the temperature the evidence is somewhat ambiguous and difficult to tie down.

So my main concern is that any paper that starts with a premise that fossil fuel usage will lead to catastrophic failure of Greenland and Antarctic ice sheets which is unacceptable to humanity will inevitavbly find evidence that this happened in the Eemian whether it did or not!

However, kudos to the authors who put up front that models are an imperfect representation of the climate system, that paleao and proxy data are riddled with ambiguities and the modern record is too short and imperfect. Nothing has changed with this paper - all three statements are still true and impact our ability to test hypotheses which is where this discussion came in.

I waited for Paul to respond first because its his speciality. I did want to reply earlier because I saw some of you reaching too pessimistic conclusions. I still think Paul is conveying an overly pessimist message. Paul has already mentioned success stories such as the detailed studies of cave speleothems in the Middle East where it can be concluded that most of the isotopic changes are due to a water effect. Surely you should infer from this that it is possible to tease out past environmental parameters. Paul's gripe is with people who don't appreciate the complexities of the proxies they use, but plough on regardless and falsely present temperature data when that may be nothing of the sort.

Some of you have been puzzled by my support of Paul's position while earlier accepting temperature data from ice cores. I'll try to explain. I, and others, use the isotope data as a temperature proxy because we believe the changes reflect temperature and other factors, but (and this is the important point) we believe those other factors are temperature dependent. Thus although absolute temperature values may be exceedingly difficult to obtain (Paul's argument) timed relative temperature changes (when coupled with dating methods on the host ice) are apparent (my argument).

So be more positive Dung, its not as you may have thought.

I am getting the distinct impression that I am playing Watson to Paul's Sherlock, trying to explain his much greater expertise.

One concern.Their models predict South Atlantic cooling and a cold spot off Greenland in 50 years Both are already visible .

Yay! Something to get your knickers in a real twist over, EM! Now, tell me – over what period was this average that these temperatures differ from determined? And how? Also, could you please tell us what these “deniers” that you gloat over are actually denying?

Alan Kendall / Paul DennisThe more I read of what you say, the more convinced I am that your approach is the correct one. Not necessarily that the conclusions you draw are correct — I am far from qualified to comment on that one way or the other — but that what you and the climate "community" are trying to do is to dig a signal out of conflicting data and that this is not an easy or a quick process.There are no glib answers.But as Golf Charlie makes clear, others in that same "community" are desperate for "a quick, easy win" whether because they genuinely believe that global warming is going to be catastrophic (Dung's 'cherished evidence') or because they fear it won't be and have their own environmentalist agenda to pursue. I am, incidentally, inclined to believe that Hansen belongs in the latter camp.Either way, nothing is happening as yet to support the extreme views, at least as far as I can see, and we would be a lot better served if governments could be persuaded to listen to cool heads rather than the hotheads which are the ones who appear to be in charge right now.

Once you sent me cheques in the post but now I am in the doghouse for cherishing some evidence; et tu Brutus?

In the time honoured (until recently) scientific method , one keeps what theories have been verified by observation or experiment and one discards the rest. The more often a theory is tested and verified the more confidence one has that it may actually turn out to be reliable. Reliable friends tend to be cherished and should they ever be proven unreliable then there will be much wailing and gnashing of teeth ^.^

Mike Jackson says - "that same "community" are desperate for "a quick, easy win" whether because they genuinely believe that global warming is going to be catastrophic [..]or because they fear it won't be and have their own environmentalist agenda to pursue."

That seems to sum up EM's posture on Climate Change fairly succinctly. He triumphantly brandishes any publication, speculation or rumour that might be interpreted by him to have concluded,suggested, implied or hypothesise that anthropogenic emissions of CO2 are causing unprecedented warming leading inevitably and rapidly to catastdrophe while dismissively rubbishing any research conclusions, climatic,paleoclimatic data or evidence that do not support his views and thus offend his deeply held convictions of impending disaster.

This posture reminds me of the reported behaviour of 17th century witch hunters.

SpectatorI'd never thought of it in terms of witch hunts but I agree with the thrust of your argument.I have never understood what I sometimes think of as "professional pessimism". Why does EM (because he is the example to hand but there are plenty of others around) apparently want their predictions of catastrophe to be right and all the cautionary work being done by the likes of ... name any one of a dozen ... to be wrong?

Show me convincing evidence that my fears are groundless and I will stop worrying.

Note that "convincing" refers to high quality peer reviewed papers in reputable journals which agree with observed data and known physics, not posts on sceptic propaganda sites or dubious papers in attack journals. I was never very good at wishful thinking.

Unfortunately the output from the climate datasets and the published literature show that AR5 is probably conservative. As more research comes in the prospect is looking worse, rather than better.

I do not think you need excessive vulcanism to end a snowball Earth episode. The onset of Snowball conditions tends to coincide with mountain building episodes and accelerated weathering, or with the appearance of photosynthetic organisms. Both produce a drawdown of CO2 to very low levels, followed by worldwide glaciation.

Once glaciated a snowball Earth has very little weathering, so drawdown of CO2 stops. Normal levels of vulcanism are enough to increase CO2 over millions of years. When the CO2 concentration is high enough to start tropical thawing the positive feedback loop of reducing ice albedo does the rest.

Yes, McCarthyism I'll go along with. But McCarthy had a readily identifiable threat and arguably a "clear and present danger" to the US.There was never any such readily identifiable threat when, for example, Wirth set up the Hansen Senate hearing in 1988, except in his own mind. McCarthy could (and did) argue that he was acting in the best interests of the US and it didn't take all that long to take him down.Wirth et al claim to be acting on behalf of "the planet". There is a difference between targeting a well-established and in many people's eyes realistic threat to the security of one's country and reviving the failed philosophy of Malthus and using natural phenomena to impose a punitive political philosophy on an unwilling world.Remember it was Wirth who said, "We've got to ride the global warming issue. Even if the theory of global warming is wrong, we will be doing the right thing in terms of economic socialism and environmental policy."Those are not the words if someone who respects the democratic process, which McCarthy did whatever his obsessions.

EMHow can we show you your fears are "groundless" when you know as well as anyone here that science simply doesn't work that way?But that in itself ought to give you pause because neither does science give you conclusive answers that your fears are realistic.I suggested in my reply to Spectator that there are dozens of people working in climate or relevant associated disciplines (Alan and Paul among them and Nick Lewis and Judith Curry) who have done work and published results that challenge the current paradigm.Increasingly we see papers challenging that paradigm especially on the sensitivity front and yet your reaction, instead of looking at what these papers say, is to rush to find something — anything — to use as a comfort blanket.Whatever the long-term effects may turn out to be none of the dire predictions about extreme weather or sea-level or tipping points of ice caps or total disaster if temperatures reach about 2° below the Holocene optimum (yes, 'below' is what I said) are happening now.So let's get a sense of proportion into this and stop behaving as if disaster is just round the corner or, if it is, that there is anything we can do about because there isn't.Unpicking the Industrial Revolution may be a sexy idea if you're an econut but for anyone else to behave as if that is the only way to save the planet (from what?) is bordering on insanity.

So my main concern is that any paper that starts with a premise that fossil fuel usage will lead to catastrophic failure of Greenland and Antarctic ice sheets which is unacceptable to humanity will inevitavbly find evidence that this happened in the Eemian whether it did or not!

This is always the scientist's dilemma. If the science suggest that there is a problem, do you become an advocate for its solution?

If you do advocate, subsequent work becaumes automatically suspect as you describe.

If you do not advocate, the problem may not be addressed.

I vaguely remember lines from "Day afterTomorrow"

Politician-You should stick to the science and leave policy to us.

Scientist-We tried that and it didn't work.

As an active climate scientist, do you feel that you should not take part in the policy debate?

If I became an active scientist again, should I stop posting comments at BH, ATTP or wherever?

Sorry Entropic man, increased volcanism not my idea. I was just quoting other people's ideas.

Don't much fancy yours either. Seem to remember snow, and eventually ice, absorbs more CO2 than warmer water. So what stops continual CO2 removal? If volcanism built up CO2 over millions of years, then some lava and pyroclastic deposites would have come to rest directly on ice. Where is the evidence for this? I would expect to find these materials to show collapse features. I don't know of any such occurrences. The only part of "your " explanation I would unreservedly accept is the effect of decreasing albedo as ice cover declined. My own guess about snowball earth is that either the sun hiccuped, or the solar system passed through a dust cloud. Nothing to do with CO2.

Completely off topic but I thought you might enjoy this. My wife just told me that our 15-year old granddaughter, who lives with us, looked over my shoulder as I was reading this thread and saw a posting that thanked me by name for my contributions. Later she expressed concern that "grandad is being groomed".

The mind boggles, I'm sure golfCharlie can have great sport with this.

Odd as it may seem, EM, but I would like you to be right… or at least partially so. I do hope that the temperatures do regain their gentle upward incline; so far, it has brought us nothing but gain, with more food being produced on less land, less consumption of fossil fuels for warmth, etc, etc. For some reason, you see these as disasters. I have asked many, many times for you to provide us with examples of disasters that can be categorically blamed on climate change; you have yet to provide any (and, no, “extreme weather events” do NOT, and never have, class as climate change, they are the vagaries of weather… you do know the difference, I hope?). I do fear that we are set for a decline in temperatures, as Piers Corbyn opines; historical record shows that falls in temperature are faster than rises, so we could be in for a shock, as a return to a little ice age (or worse) would be considerably worse than any increase. Your Morton’s Demon is truly doing a sterling job; ALL the evidence (i.e. steadily rising CO2, temperatures rising not so much) is that CO2 is not, nor ever has been, the driving factor in temperature or climate.

Read what Mike Jackson is writing, and reflect on the import of the message: those whose words you cleave to are not scientific nor are they democratic, and the future that they promise is not one that many of us would want.

EM: please be honest – you have admitted to being a teacher of a science (biology); that does not necessarily make you a scientist. Patrick Moore, for all his zeal about the stars, never claimed to be an astronaut (though no doubt would have loved to have been one).

Yes, McCarthyism I'll go along with. But McCarthy had a readily identifiable threat and arguably a "clear and present danger" to the US.Mar 23, 2016 at 12:52 PM | Registered CommenterMike Jackson

I'm not sure about that. McCarthy rode a wave of paranoia that was already there and existed before and after his presence. As a senator, he had no connection with the House Committee on UnAmerican Activities, for example.

The USA had (still has) collectively an immense fear of the outside world, which partly explains its anti-commie nightmares of the 40's and 50's. It's, at very least, debatable to what extent the USA was significantly menaced at the time.

Part of the US fear of socialism/communism stemmed from racial fears emanating from the Deep South (see Elaine massacre), where early civil rights activity was equated with socialist uprising. The FBI tracked Martin Luther King to the end.

McCarthy went for homos as well as for commies (plus of course non commies alleged to be such).

Paul Dennis and Alan Kendall, thank you again, for your expertise and insight.

It again reminds me of some of the miscarriages of justice, exposed years after the trial. The police 'believed' they knew who the guilty party was, and then had to 'find' evidence to fit. Some members of the public have proved vulnerable to suggestions about changing the slant of their evidence, some paid professional experts have been relaxed about finding the correct evidence, and ignoring that which conflicts.

It is good to know that experts are still able to report on the evidence they have, rather than 'best fitting' it to a a predetermined verdict. In my cynical experience, they are more trustworthy!

Martin ASorry, I never meant to imply that the good ol' U S of A wasn't in the grip of one of its periodic bouts of paranoia or that McCarthy didn't take full advantage.My point was simply that on the basis that "just because you're paranoid doesn't mean they aren't out to get you" worries about Communists and communist infiltration had at least some roots in reality.There is more than a touch of McCarthyism around at the moment but even less justification than could be explained by the aftermath of WW2.(Remember the Americans knew at first hand what nuclear weapons could do and with their own citizens passing information to the Soviet Union a touch of paranoia might be forgiveable!)